Regulation of dynamic recrystallization in p-type Bi2Te3-based compounds leads to high thermoelectric performance and robust mechanical properties

Abstract

Bi₂Te₃-based bulk materials are the best commercially available thermoelectric materials for near room temperature applications. However, the poor mechanical properties of zone melting material and inferior thermoelectric performance of powder metallurgical material restrict their large scale deployment. In this study, p-type Bi₂Te₃-based materials were prepared using the hot extrusion technique, and the underlying mechanisms for microstructure evolution were revealed. The hot extrusion speed significantly impacts the strain rate, an indicator to modulate the dynamic recrystallization (DRX) and grain growth, thereby effectively regulating the microstructures of samples. For the sample extruded at a speed of 1.0 mm min⁻¹, the refined grain with an average grain size of 1.53 μm and an orientation factor F₍₁₁₀₎ of 0.28 is achieved. This highly textured structure and high-density low-angle boundaries (LAGBs) maintain the high carrier mobility of 264 cm² V⁻¹ s⁻¹, comparable with the zone melting sample. In contrast, increasing grain boundaries, dislocations, and inherent point defects intensifies the phonon scattering and suppresses the lattice thermal conductivity to 0.73 W m⁻¹ K⁻¹. All these contribute to a practical high ZT value of 1.1 at room temperature. Moreover, the fine grains and high-density dislocations ensure robust mechanic properties with a compressive strength of 189 MPa and a bending strength of 139 MPa, which is a guarantee for the successful cutting of microparticles with dimensions of 100 × 100 × 200 μm³. The fabrication of high-quality materials with both high thermoelectric performance and strong mechanical properties paves the way for the miniaturization of thermoelectric modules.